Re: [Patch v2 2/2] mm/page_alloc: not necessary to multiply MAX_NODE_LOAD

[Vlastimil Babka <vbabka@suse.cz>]

On 4/9/22 01:07, Wei Yang wrote:
> On Fri, Apr 08, 2022 at 10:09:48AM +0200, David Hildenbrand wrote:
>>On 08.04.22 04:59, Wei Yang wrote:
>>> Since we just increase a constance of 1 to node penalty, it is not
>>> necessary to multiply MAX_NODE_LOAD for preference.
>>> 
>>> This patch also remove the definition.
>>> 
>>> [vbabka@suse.cz: suggests]
>>> 
>>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>>> CC: Vlastimil Babka <vbabka@suse.cz>
>>> CC: David Hildenbrand <david@redhat.com>
>>> CC: Oscar Salvador <osalvador@suse.de>
>>> ---
>>>  mm/page_alloc.c | 3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>> 
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 86b6573fbeb5..ca6a127bbc26 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -6170,7 +6170,6 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write,
>>>  }
>>>  
>>>  
>>> -#define MAX_NODE_LOAD (nr_online_nodes)
>>>  static int node_load[MAX_NUMNODES];
>>>  
>>>  /**
>>> @@ -6217,7 +6216,7 @@ int find_next_best_node(int node, nodemask_t *used_node_mask)
>>>  			val += PENALTY_FOR_NODE_WITH_CPUS;
>>>  
>>>  		/* Slight preference for less loaded node */
>>> -		val *= (MAX_NODE_LOAD*MAX_NUMNODES);
>>> +		val *= MAX_NUMNODES;
>>>  		val += node_load[n];
>>>  
>>>  		if (val < min_val) {
>>
>>I feel like this should be squashed into the previous patch. It has the
>>same effect of making this code independent of nr_online_nodes. And I
>>had to scratch my head a couple of times in patch #1 why the change in
>>patch #1 is fine with thus remaining in place.
>>
>>
>>Having that said, I consider this code highly unnecessary
>>over-complicated at first sight. Removing some of the magic most
>>certainly is very welcome.
>>
>>This semantics of the global variable node_load[] remains mostly
>>mysterious for me.

Looks like after this patch(es), it would be "how many times was this node
picked as the first fallback out of nodes with the same distance"?

>>
> 
> So the suggestion is a v3 with #1 and #2 squashed?

Yes, and I agree with the suggestion.

>>-- 
>>Thanks,
>>
>>David / dhildenb
>